Tesofensine Side Effects and Safety Profile

Key takeaways

• The most common side effects are dry mouth, insomnia, constipation, and nausea
• The biggest safety signal is elevated heart rate: +7.4 bpm at the 0.5 mg dose in Phase 2 data [1]
• Blood pressure was not significantly affected at the 0.5 mg dose
• Adding metoprolol (as in the Tesomet formulation) appears to neutralize the heart rate increase [2]
• GI side effects are milder than those seen with GLP-1 receptor agonists
• Long-term safety data beyond 24 weeks is limited

Understanding the side effect profile

Tesofensine works by blocking the reuptake of three neurotransmitters: serotonin, dopamine, and noradrenaline. Each of these pathways contributes to appetite suppression and increased energy expenditure, but each also carries its own set of potential side effects [1].

The safety data comes primarily from two sources: a Phase 2 trial of 203 obese adults published in The Lancet (Astrup et al., 2008) [1] and a smaller randomized trial of 21 adults with hypothalamic obesity (Huynh et al., 2022) [2].

This is a drug still in clinical development. It is not FDA-approved for any indication. The side effect data here reflects clinical trial observations, not post-marketing surveillance from millions of patients. That distinction matters.

Common side effects

Dry mouth

Dry mouth was the most frequently reported side effect across tesofensine studies. In the hypothalamic obesity trial, 43% of participants on Tesomet reported dry mouth versus 0% on placebo [2].

This makes pharmacological sense. Both noradrenaline and serotonin reuptake inhibition reduce salivary gland output. The effect is usually manageable but persistent throughout treatment.

Insomnia and sleep disturbances

Sleep problems affected 50% of Tesomet-treated patients in the hypothalamic obesity trial, compared to 13% on placebo [2]. Noradrenaline reuptake inhibition increases arousal and can make it harder to fall asleep or stay asleep.

In the Phase 2 trial, insomnia was listed among the most common adverse events, though specific rates by treatment group were not broken out separately [1].

Constipation and hard stools

GI effects were present but generally milder than what patients experience with GLP-1 medications. The Phase 2 trial reported constipation, hard stools, and diarrhea as common adverse events. Nausea was also reported, though at lower rates than typically seen with semaglutide or tirzepatide [1].

Headache

In the hypothalamic obesity trial, 36% of Tesomet patients reported headaches compared to 0% on placebo [2]. This was generally mild and tended to occur early in treatment.

Cardiovascular effects: the main safety concern

The heart rate signal is the most important safety consideration with tesofensine. Here’s what the data shows.

Heart rate

In the Phase 2 trial, tesofensine 0.5 mg increased resting heart rate by 7.4 beats per minute compared to placebo (P = 0.0001) [1]. The 0.25 mg dose did not produce a statistically significant heart rate increase. The 1.0 mg dose produced larger increases, which is one reason that dose was not carried forward [1].

An increase of 7.4 bpm may sound small, but sustained heart rate elevation has been a red flag for weight loss drugs historically. Sibutramine was withdrawn from the market in 2010 partly due to cardiovascular events linked to heart rate and blood pressure increases [3].

Blood pressure

At the 0.5 mg dose, neither systolic nor diastolic blood pressure showed significant changes compared to placebo [1]. This is an important distinction from sibutramine, which raised both heart rate and blood pressure.

The Tesomet solution

To address the heart rate concern, Saniona developed Tesomet: a combination of tesofensine 0.5 mg with metoprolol 50 mg (a beta-blocker). In the hypothalamic obesity trial, this combination showed no significant differences in heart rate or blood pressure between treatment and placebo groups [2].

A 2013 animal study also demonstrated that antihypertensive treatment preserved the appetite-suppressing effects of tesofensine while preventing cardiovascular side effects, supporting the rationale for this combination approach [4].

Side effects compared to other weight loss drugs

vs. GLP-1 receptor agonists

The side effect profiles barely overlap. GLP-1 drugs like semaglutide and tirzepatide primarily cause gastrointestinal side effects: nausea (up to 44%), vomiting, diarrhea, and constipation. These GI effects are dose-limiting for many patients.

Tesofensine’s main issues are neurological and cardiovascular: dry mouth, insomnia, and heart rate changes. Patients who can’t tolerate the GI effects of GLP-1 medications might tolerate tesofensine better, and vice versa.

For more on GLP-1 side effects, see our guides on peptide side effects and what happens when you stop Ozempic.

vs. phentermine

Phentermine primarily increases noradrenaline release. It causes similar stimulant-type effects: insomnia, dry mouth, increased heart rate, and elevated blood pressure. Tesofensine’s triple-reuptake mechanism means it also affects serotonin and dopamine pathways, which adds appetite suppression through different circuits but also adds the potential for mood-related side effects [5].

vs. naltrexone-bupropion (Contrave)

Contrave also targets multiple neurotransmitter systems. Bupropion inhibits dopamine and noradrenaline reuptake (similar to two of tesofensine’s three targets). Common Contrave side effects include nausea, headache, constipation, and insomnia. The overlap with tesofensine’s profile is substantial, which makes sense given the shared pharmacological targets.

Who should avoid tesofensine

Based on the available clinical data and the drug’s mechanism of action, tesofensine would likely be contraindicated in:

• Patients with uncontrolled hypertension or tachycardia
• Anyone taking MAO inhibitors (risk of serotonin syndrome)
• Patients with a history of cardiovascular events (heart attack, stroke)
• People taking other serotonergic medications (SSRIs, SNRIs) due to potential interactions
• Patients with severe anxiety or insomnia, given the noradrenergic stimulation

These are reasonable precautions based on the drug’s pharmacology, not formal contraindications from an FDA label (since no FDA label exists).

What we don’t know yet

The honest answer is that a lot of safety questions remain open:

Long-term cardiovascular outcomes. The Phase 2 trial lasted 24 weeks. We don’t know what happens to heart rate and cardiovascular risk over 1-2 years of continuous use [1].

Psychiatric effects. Drugs that modify serotonin, dopamine, and noradrenaline activity can affect mood, anxiety, and cognition. The clinical trials were too small and too short to detect rare psychiatric events. One participant in the hypothalamic obesity trial discontinued due to exacerbated pre-existing anxiety [2].

Drug interactions. Formal drug interaction studies haven’t been published. Given that tesofensine affects three major neurotransmitter systems, the potential for interactions with antidepressants, stimulants, and other CNS-active drugs is significant.

Abuse potential. Drugs that increase dopamine signaling can carry abuse liability. This hasn’t been formally assessed for tesofensine, though the dopamine reuptake inhibition is weaker than that of drugs like methylphenidate or cocaine [5].

Weight regain after stopping. The appetite study showed that satiety scores returned to baseline after drug withdrawal [6], which suggests weight regain is likely. But we don’t have formal discontinuation data.

The expression of concern on the 2008 Lancet trial

One detail worth noting: The Lancet published an expression of concern regarding the Astrup 2008 trial in 2013. The expression related to concerns about data integrity, not about the safety findings per se. The study has not been retracted, and its findings remain cited in the medical literature [1].

Transparency requires mentioning this. It doesn’t invalidate the safety data, but it adds a layer of uncertainty to the evidence base.

Frequently asked questions

Does tesofensine raise blood pressure?▼

At the 0.5 mg dose in Phase 2, systolic and diastolic blood pressure were not significantly different from placebo [1]. The Tesomet formulation, which adds metoprolol, showed no blood pressure increases in the hypothalamic obesity trial [2].

How serious is the heart rate increase?▼

The 7.4 bpm average increase at 0.5 mg is clinically meaningful for a weight loss drug, which is why the Tesomet combination includes metoprolol. For context, a resting heart rate increase of this magnitude has been associated with elevated cardiovascular risk in epidemiological studies, though whether that applies to drug-induced increases over months of treatment is debated [1].

Can you take tesofensine with antidepressants?▼

No published data addresses this directly. Given that tesofensine inhibits serotonin reuptake, combining it with SSRIs or SNRIs would theoretically increase the risk of serotonin syndrome. This combination should be avoided until formal interaction data is available.

Is tesofensine safer than phentermine?▼

The data isn’t sufficient for a direct comparison. Tesofensine may produce more weight loss [1], but its cardiovascular profile (particularly heart rate elevation) is a concern. Phentermine has decades of post-marketing safety data; tesofensine has only Phase 2 trial data from a few hundred patients.

Are the side effects dose-dependent?▼

Yes. The Phase 2 trial showed a clear dose-response for both efficacy and adverse events. The 1.0 mg dose produced more weight loss but also more side effects, which is why 0.5 mg was selected as the optimal dose [1].

What happened to the Phase 3 trial?▼

Phase 3 trials for general obesity were delayed due to financial challenges at NeuroSearch (now Saniona). The company has since refocused on rare indications like hypothalamic obesity and Prader-Willi syndrome, where the unmet need is high and smaller trial populations are acceptable [2].

References

1. Astrup A, Madsbad S, Breum L, et al. Effect of tesofensine on bodyweight loss, body composition, and quality of life in obese patients: a randomised, double-blind, placebo-controlled trial. Lancet. 2008;372(9653):1906-1913. https://pubmed.ncbi.nlm.nih.gov/18950853/

2. Huynh K, Klose M, Krogsgaard K, et al. Randomized controlled trial of Tesomet for weight loss in hypothalamic obesity. Eur J Endocrinol. 2022;186(6):687-700. https://pubmed.ncbi.nlm.nih.gov/35294397/

3. Derosa G, Maffioli P. Anti-obesity drugs: a review about their effects and their safety. Expert Opin Drug Saf. 2012;11(3):459-471. https://pubmed.ncbi.nlm.nih.gov/22439841/

4. Hansen HH, et al. Anti-hypertensive treatment preserves appetite suppression while preventing cardiovascular adverse effects of tesofensine in rats. Obesity. 2013;21(5):985-992. https://pubmed.ncbi.nlm.nih.gov/23784901/

5. Heal DJ, Gosden J, Smith SL. Centrally acting agents for obesity: past, present, and future. Drugs. 2018;78(11):1113-1132. https://pubmed.ncbi.nlm.nih.gov/30014268/

6. Gilbert JA, Gasteyger C, Raben A, et al. The effect of tesofensine on appetite sensations. Obesity. 2012;20(3):553-561. https://pubmed.ncbi.nlm.nih.gov/21720440/

7. George M, Rajaram M, Shanmugam E. New and emerging drug molecules against obesity. J Cardiovasc Pharmacol Ther. 2014;19(1):65-76. https://pubmed.ncbi.nlm.nih.gov/24064009/

8. Bhatt DK, et al. Tesofensine, a novel antiobesity drug, silences GABAergic hypothalamic neurons. PLoS ONE. 2024;19(4):e0301826. https://pubmed.ncbi.nlm.nih.gov/38656972/